1. Field of the Invention
This invention relates to a system for generating a signal which is representative of the speed of rotation of a synchro while using a first digital signal which is proportional to the sine of the angle of rotation of the shaft of the synchro, and a second digital signal which is proportional to the cosine of said angle.
2. Description of the Prior Art
The signals which correspond to the speed of rotation of the synchro are used in many fields of application, particularly for aircraft which are not provided with a device for indicating their vertical speed. In this case signals are utilized originating from a synchro (driven by a barometric altimeter) the speed of rotation of which is proportional to the vertical speed H.sub.B of the aircraft.
In a known system an analog method is used for deriving the output voltage for generating the speed signal, which causes problems as regards with respect to the sensitivity, the phase distortion, the harmonic distortion of the output noise and the excitation voltage of the synchro.
To avoid the difficulties encountered when generating a signal which is equal to the derivative of an analog signal, it is possible to use the digital sine and cosine signals for calculating the tangent of the angle of rotation of the shaft of the synchro and the derivative of the tangent. As the tangential function is only linear for small angles it is impossible to approach this derivative by means of a first term of a series expansion but several terms must be used, which requires a complicated circuit.